The present application relates to a device and to a process for the continuous discharge of pre-classified rubber particles from a gas phase polymerization reactor.
A The no polymerization of polyolefins in the gas phase is a process which is by no means new and was carried out for the first time on an industrial scale as early as 1968 (Ullmanns Encyclopaedia of Industrial Chemistry, 4th edition 1980, vol. 19, p. 186 ff)
In this process, the actual polymerization reaction takes place in a fluidized bed reactor which is composed of a reaction zone and an overlying calming zone in which the solids particles are largely separated from the gas phase. The monomers, the catalyst and possible additives such as, e.g., additives or fillers, are introduced into the reaction zone. In order to maintain a fluidized bed, a circulating gas stream is fed to the reactor from below. This circulating gas stream, which is composed substantially of the unreacted monomers, is drawn off again at the top of the reactor, residual particles are removed, the gas is cooled and returned to the reactor. The polymer produced is discharged continuously or batchwise from the reaction zone and undergoes further treatment.
Several processes for discharging polymers from a gas phase polymerization reactor are known from the prior art.
According to U.S. Pat. No. 3,023,203, for example, the discharge of polymer particles from a gas phase polymerization reactor is carried out with an extruder. The extruder is joined to the lower end of the polymerization reactor by means of a pipe.
A process for discharging polymers from a gas phase polymerization reactor with a screw extruder is known from EP-A-0 348 907, which extruder is joined to the gas phase reactor either directly or by means of a receiving vessel.
Both procedures have the disadvantage that all the particles, regardless of their size, which collect at the lower end of the reactor, are discharged without being classified.
Moreover, a process for discharging polymer particles from a gas phase react or is known from EP-A-0 728,771, wherein,the particles are discharged batchwise by means of two cycled rotary feeders. This process also has the disadvantage that the polymer particles are discharged without being classified. Moreover, due to the cycled discharge of the polymer particles, pressure fluctuations in the gas phase reactor occur with this process.
The object was, therefore, to provide a,process for the continuous discharge of pre-classified polymer particles frog a gas phase polymerization reactor which does not, have the disadvantage of the prior art. Further object of the present invention is to provide a device for the continuous discharge of pre-classified polymer particles from a gas phase polymerization reactor.